Most people do not realize the extent to which composites are part of our everyday lives. Why have they invaded our home, our automobiles and our places of work? There are many reasons, but before we get into them, let us be clear about what we mean when we use the word composites. In today's context, composites are a layers of a reinforcing material bonded together with a chemical compound.
Components of Composites
That chemical compound can range from cement through to exotic, expensive polymeric chemical resins which have to be cured in an autoclave (pressurized oven). The reinforcing materials in use range from rebar (steel) or wire mesh in the case of concrete and cement to hi-tech fibers such as aramid fiber and carbon nanotubes. In between lie a vast range of 'everyday' reinforcing - even wood and cotton are used.
Here, we are not concerned with reinforced concrete, which lacks several of the key advantages of hi-tech composites. Everyone knows about GRP (Glass reinforced polymer) - 'fiberglass' - and anyone will probably find the material within ten feet of where they are sitting right now. GRP is at the simpler end of the hi-tech composites spectrum.
Why use Composites?
In today's world, there are three main reasons. One is financial, translating ultimately to profit. This may come through a performance improvement which makes a product more attractive or economic to own, or when a service becomes cheaper to deliver (or more profitable).
The second is legislative, driven by environmental protection factors. The world's most environmentally friendly airliner, the Boeing Dreamliner, uses 32 tons of composites in its construction. Its development was driven in large part by environmental legislation trends and increasing fuel prices. It could not fly without composites.
The third reason is, simply, because there is no alternative - the Apollo mission could not have got to the moon without composites used in the suits the astronauts wore. So, there are three advantages right there - and we have not started on the technology yet. In fact, all the technology advantages fall under one of those three categories - economic, legal or 'no alternative'.
Strength to Weight Ratios
Those factors for choosing composites sound reasonable, but what are the fundamental properties of composites that mean there is no alternative in many cases? One key advantage of many composites is their strength compared to their weight. Without getting right down to the physics, let us compare a few materials using the accepted measure of specific strength (which takes into account the density of the material):
Material - Specific Strength
Spider silk - 1069
Carbon epoxy composite - 785
Stainless steel - 254
Concrete - 4.4
Mother Nature wins there, but when we look at a carbon fiber such as used in a composite, then its specific strength is twice that of spider silk. The latest carbon technology - carbon nanotubes - have a specific strength of the order of 46,000 on the same scale!
Is it any wonder then why any flying machine or spacecraft uses as much composite as possible? Anything mechanical that moves needs energy to move it, and the lighter it is, then the less energy needed. With energy costs going the way they are, we can easily see why composites are used increasingly in autos, bicycles and boats.
Composites are fairly inert - they do not rust, they do not directly suffer galvanic (electrical) corrosion caused by stray currents and they can easily be formulated to resist ultra violet radiation. Some epoxies can be affected by chemicals, but those aggressive solvents are few and far between.
Whatever the durability concern - flexibility, impact resistance, abrasion resistance - then there is a composite that will suit the purpose. And if not, then one can be designed.
The range of composite today is such that if there is not one for a specific project, then it can probably be designed using an appropriate resin and reinforcing material.
Construction Convenience and Style
Using molds for laminating and production processes such as rotational molding and extrusion, then engineering properties can be tailored. Beyond that, look at a carbon fiber tennis racquet or a snowboard and you can see the smooth, good looking products that the technology is capable of.
The Way Forward
We mentioned carbon nanotubes, but beyond that we see graphene sheets coming, and higher specification resins. We covered the reasons for using composites, bar one - competition. Most consumer and industrial goods manufacturers today have to look at using composites in their products, or they will become uncompetitive. Shoes or ships, tables or tools - composites are here to stay.